An electric power steering device for automobile is configured to detect the rotation direction and rotation torque of a steering shaft rotated by a driver operating a steering wheel, and drive an electric motor so as to rotate in the same direction as the rotation direction of the steering shaft on the basis of the detected value, to generate steering assist torque.
Conventionally, the motor drive control device for electric power steering which performs drive control of a motor used in an electric power steering device adopts, as a small-sized and highly-reliable structure, a stacking structure having a storage space which is formed by a lid and a housing and stores: a power conversion circuit unit in which a smoothing capacitor and a MOSFET as a semiconductor switch configuring the drive control are arranged on the same metal substrate; a control circuit unit in which control circuit components such as a microcomputer are arranged; and a filter unit in which a filter is arranged (see, for example, FIG. 2 in Patent Document 1).
In another example of stacking structure, an upper-side cover and a lower-side heatsink sandwich therebetween: a control board on which surface mounted components for control circuit are mounted to form a control circuit; a power board on which surface mounted components for power are amounted; and a connector case located between the control board and the power board and integrated with an external-connection connector for connecting to the outside such as a power supply system or another ECU (see, for example, FIG. 2 in Patent Document 2).